Naegleria fowleri (N.f.) is a free-living ameba belonging to the family Vahlkampfiidae. This ameba is responsible in humans for a serious pathological condition, which is very fortunately extremely rare (235 cases detected in 2007): primary amebic meningoencephalitis (PAM) (Cervantes-Sandoval I, 2008; Kemble S K, 2012; TW, 2010; Su M Y, 2013). Infection with these free-living amebae has a catastrophic prognosis in approximately one week and a few weeks with antibiotic treatment (Su M Y, 2013). There is no truly effective treatment against this infection; very fortunately, the diseases is rare and requires the coming together of specific conditions in order to trigger PAM. These particular conditions and also the inoculum required are still unknown at the current time. However, some drugs and antibiotics appear to influence the progression of the infection, such as amphotericin B, rifampicin and miconazole which, when combined, have proved to be effective on 2 or 3 individuals. In 1992, the literature reported only 7 cases of proven survival after PAM (Gautam P L, 2012) and only in very young subjects from 2 to 14 years old and in whom the treatment and the infection left more or less significant neurological after effects. The survival rate is therefore even lower than for infection with the Ebola virus. Thus, the monitoring and control of this free-living ameba constitute an increasingly significant preoccupation.
Generally, it is known that Naegleria fowleri has a ubiquitous distribution in the environment (Martinez A J, 1997), since this ameba has been isolated from the soil, river water and lake water (Jamerson M, 2009) or industrial wastewater, and biofilms (Goudot S, 2012; S. A. Huws, 2005), characteristics that it shares with other free-living amebae. Several potentially pathogenic bacteria, including Legionella pneumophila, have developed mechanisms for surviving and replicating inside free-living amebae (Huang S W, 2010; De Jonckheere, 2011). Furthermore, it has been demonstrated that nuclear power stations greatly contribute to the development of the ameba Naegleria fowleri through the reheating of river water by several degrees. Indeed, the ameba Naegleria fowleri is thermophilic with development temperature ranges of from 25° C. to 45° C. (Visvesvara G S, 2007).
EDF, which operates more than 11 nuclear power stations in France, has quantified the risk relating to the level of Naegleria fowleri detected in water. In order to have a better understanding of this risk, the Department of Studies and Research and the Department of Medical Studies of EDF have calculated the risks of death from PAM when swimming, as a function of the concentration of Naegleria fowleri in the water. This risk can be broken down in the following way:
risk for 1 swim=probability of inhaling “n” Naegleria fowleri when swimming in water where Naegleria fowleri are present at a concentration “c” (10 ml of water inhaled per swim)
multiplied by
probability of death when “n” Naegleria fowleri have been inhaled (modeling according to animal data).
When choosing the normal log model, which gives the lowest estimations, and which fits well with the actual data (USA, Australia, New Zealand), the following risks are obtained:
Concentration Risk for an Amount n of N.f. In Swimming Water                1 Naegleria fowleri/liter, risk=10-8, i.e. one death per 100 million swims        10 Naegleria fowleri/liter, risk 1.45×10−7, i.e. one death per 7 million swims        100 Naegleria fowleri/liter, risk=7.24×106, i.e. one death per 140 000 swims        1000 Naegleria fowleri/liter, risk=1.34×10−3, i.e. one death per 746 swims.In accordance with the recommendations of the Conseil supérieur d′hygiène publique de France (CSHPF) [French High Council for Public Hygiene], the exceeding of the limiting value of 100 Naegleria fowleri (N.f.) per liter must result in swimming being prohibited (cf. in particular the opinion of the CSHPF of May 4, 2004, relating to the feedback from experience of the antiamebic treatments with monochloramine carried out in 2003 by EDF on the electricity-producing nuclear power stations (CNPE) of Bugey, Chooz, Dampierre, Golfech and Nogent).        